Agnon's massive, not-quite-finished novel about a German-Jewish scholar's adultery, set in British-occupied Jerusalem in the late 1930s, is a yeasty mix of realism and allegory. In this, his last major work, the Israeli Nobel laureate portrays Manfred Herbst, distinguished Byzantine specialist at Hebrew University, a married man with four children who has an obsessive affair with a blunt, bossy young nurse named Shira. Though her name means ``poetry,'' she is neither pretty nor intellectual, and seems an unlikely object for his affections, yet his liaison with this sickly woman (she develops leprosy) jolts him out of his ivory-tower mentality. Capturing the Jewish refugees' precarious, day-to-day existence in Palestine, the growing menace of Hitler and the rising wave of Arab attacks, the long, digressive narrative is thick with the tales of immigrants, with often ironic philosophical nuggets and with Herbst's reflections, dreams and sadomasochistic fantasies as he transposes Byzantine decadence and splendor onto a world being overtaken by genocidal horror. (Oct.)